Wholly aromatic polyester resins long have been known. For instance, p-hydroxybenzoic acid homopolymer and copolymers have been provided in the past and are commercially available. Those wholly aromatic polyesters normally encountered in the prior art have tended to be somewhat intractable in nature and to present substantial difficulties if one attempts to melt process the same while employing conventional melt processing procedures. Such polymers commonly are crystalline in nature, relatively high melting or possess a decomposition temperature which is below the melting point. Molding techniques such as compression molding or sintering may be utilized with such materials; however, injection molding, melt spinning, etc., commonly have not been viable alternatives or, when attempted, commonly have been accomplished with difficulty. Such polymers commonly cannot be melt extruded to form nondegraded fibers. Even those wholly aromatic polymers which exhibit a melting point below their decomposition temperature commonly melt at such high temperatures or have such extremely high melt viscosities that employment of these polymers in molding or extrusion processes to obtain a quality product is a complicated matter and in some instances almost impossible. For instance, fibers melt extruded at extremely high temperatures commonly possess a voidy internal structure and diminished tensile properties.
Representative publications which discuss wholly aromatic polyesters include: (a) Polyesters of Hydroxybenzoic Acids, by Russell Gilkey and John R. Caldwell, J. of Applied Polymer Sci., Vol. II, Pages 198 to 202 (1959), (b) Polyarylates (Polyesters From Aromatic Dicarboxylic Acids and Bisphenols), by G. Bier, Polymer, Vol. 15, Pages 517 to 535 (August 1974), (c) Aromatic Polyester Plastics, by S. G. Cottis, Modern Plastics, Pages 62 to 63 (July 1975) and (d) Poly(p-Oxybenzoyl Systems): Homopolymer for Coatings; Copolymers for Compression and Injection Molding, by Roger S. Storm and Steve G. Cottis, Coatings Plast. Preprint, Vol. 34, No. 1, Pages 194 to 197 (April 1974). See also U.S. Pat. Nos. 3,039,994; 3,169,121; 3,321,437; 3,553,167; 3,637,595; 3,651,014; 3,723,388; 3,759,870; 3,767,621; 3,787,370; 3,790,528; 3,829,406; 3,890,256; and 3,975,487.
Prior attempts to obtain a melt processability from a wholly aromatic polyester have centered upon synthesizing a polyester from certain specifically defined monomer units which when incorporated into a single polymer in certain molar proportions yield a polyester capable of being melt processed. Illustrations of such polymers may be found in U.S. Patent Application Ser. No. 686,189, filed May 13, 1976, by Gordon W. Calundann, entitled "Improved Melt Processable Thermotropic Wholly Aromatic Polyester and Process for Its Production", and U.S. Patent Application Ser. No. 789,374, filed Apr. 20, 1977, by Gordon W. Calundann, Herbert L. Davis, Frederick J. Gorman, and Robert M. Mininni, entitled "Improved Melt Processable Thermotropic Wholly Aromatic Polyester Which Is Particularly Suited for Fiber Formation," both of which are herein incorporated by reference.
The polyesters described in both of these applications exclude a terephthalic acid moiety since such would destroy the melt processability of the polyester.
The exclusion of the terephthalic acid moiety from the aromatic polyester, however, may hinder the optimization of certain properties, such as tensile strength, impact strength, thermal stability, stability over longterm high temperature use, and modulus, which the terephthalic acid moiety helps to achieve.
In some instances it is possible to achieve melt processability of a wholly aromatic polyester, such as polyresorcinol phthalate which employs terephthalic acid, by utilizing specific molar ratios of isophthalic and terephthalic acid as illustrated by U.S. Patent Application Ser. No. 822,579, filed Aug. 8, 1977, by Charles E. Kramer, entitled "Melt Polymerization Process for Preparing Melt Processable Resorcinol Phthalate Polyester Utilizing a Metal Acetate Catalyst," herein incorporated by reference. The terephthalic acid content of the polyester prepared in accordance with this process, however, is held to a minimum (i.e., not greater than 30%) and consequently the optimization of physical properties as described above, such as tensile strength, impact strength and modulus, which results when terephthalic acid is present in said polyester at higher molar ratios is difficult to achieve.
It has been observed that certain phosphorus esters may be utilized as flame retardants as illustrated by U.S. Pat. Nos. 3,761,543 and 3,027,349.
It is an object of the present invention to provide a melt processable wholly aromatic polyester containing composition utilizing a normally non-melt processable wholly aromatic polyester.
It is a further object of the present invention to provide a process for rendering certain normally non-melt processable aromatic polyesters capable of being melt processed without deleteriously affecting the integrity of the polymer.
It is a still further object of the present invention to provide a wholly aromatic polyester containing composition, having a reduced melt viscosity for improved processability.
These and other objects as well as the scope, nature and utilization of the invention will be apprent to those skilled in the art from the following description and appended claims.